Our distant cousins just got a little more distant.
A new study suggests that modern humans and our closest relatives, the Neanderthals, may have split 800,000 years ago, hundreds of thousands of years earlier than had been thought.
How do scientists know this? The truth is in the teeth: Anthropologist Aida Gomez-Robles of University College London analyzed 400,000-year-old teeth from a Neanderthal ancestor, which had been discovered in a cave in Spain.
She determined that the choppers weren't at all similar to modern humans' teeth, which they should have been if the two species had been together at that time. The "teeth are very different from those that we would expect to find in their last common ancestral species with modern humans," Gomez-Robles said, "suggesting that they evolved separately over a long period of time (before that) to develop such stark differences."
The most recent common ancestor of Neanderthals and modern humans must have lived well before this time, probably hundreds of thousands of years earlier, according to New Scientist.
The study concludes that any divergence between Neanderthals and modern humans after 800,000 years ago would require "unusually and unlikely rapid dental evolution" in the teeth discovered in Spain.
The findings differ from studies of ancient DNA and cranial features, which point to a 400,000-year divergence date.
Neanderthals were a species of ancient humans that went extinct about 40,000 years ago. Modern humans share a common ancestor with Neanderthals, the extinct species that were our closest prehistoric relatives.
How close? Neanderthals and modern humans share more than 99% of their DNA.
The details on when and how two species diverged remain a matter of intense debate within the anthropological community.
Smithsonian Institution paleoanthropologist Rick Potts is far from convinced that rates of dental evolution are as standard or predictable as the new study suggests.
"She's bitten off an interesting topic here, but I just don't see the argument that dental rates of evolution are absolutely known to the point where we can then say that for certain the Neanderthal-modern human divergence must have been earlier than 800,000 years ago," Potts told Smithsonian magazine.
The study was published in the peer-reviewed journal Science Advances, a publication of the American Association for the Advancement of Science.
This article originally appeared on USA TODAY: Neanderthals split from modern humans much earlier than thought, study suggests